1. Field of the Invention
The present invention relates to photovoltaic power generation systems and methods of controlling such photovoltaic power generation systems. More particularly, the present invention concerns photovoltaic power generation systems that are constructed to prevent an intruder, who is attempting to intrude into a restricted area including an area in which solar cells are installed, from receiving an electric shock, and methods of controlling such photovoltaic power generation systems.
2. Related Background Art
In recent years, awareness of environments is spreading across the world. Among others, serious concerns are exhaustion of fossil fuels and the like and global warming due to CO2 emissions, so that the desire for clean energy is growing increasingly. Attention is thus being directed toward photovoltaic energy, which is clean energy resulting from direct conversion of solar energy to electric power, and solar cells are quickly spreading in use in various consumer-oriented fields.
In general solar cell modules possess sufficient electric insulation and enough safety to prevent an electric shock hazard even if a man should touch them. The solar cell modules are thus commercially available and are beginning to spread, but the solar cell modules involve an issue of still high cost, because a lot of coatings and insulators need to be used for ensuring the safety. Consequently, they are still unsatisfactory for application of solar cells high in power generation cost to power plants and thus are not used widely. On the other hand, there is a danger that an electric shock hazard may occur when a person except for a manager intrudes into a hazard controlled area in the power plants and the like, and it can extend to an accident in the electric power system. For eliminating this risk, studies have been made heretofore on various intrusion detecting devices and safety devices.
For example, an intruder detecting device described in Japanese Patent Publication No. 63-67718 is an intrusion detecting device composed of an outer detector placed around facilities, though not a power generation plant, and functioning to detect a passing object, an inner detector placed between the outer detector and the facilities and around the facilities and functioning to detect a passing object, an outer detecting circuit and an inner detecting circuit each having a filter for passing only frequencies caused by passage of a manager or a person concerned, among output of the outer and inner detectors, and a level detector for detecting only vibration levels due to a man, and an intrusion detecting circuit for counting output of the outer or inner detecting circuit and producing an intrusion detection signal when a count reaches a predetermined value within a given time.
Conventionally, studies were conducted on methods of preventing intrusion of an intruder or on methods of detecting an intruder by making use of the monitoring method as described above. In the conventional power plants such as thermal power plants, atomic power plants, and so on, however, if the system is brought once to a halt, a considerable time will be required for a restart of the system and thus the halt will cause great disadvantage. Therefore, there was no conception that the entire power generation system was brought to a halt as a safeguard against intruders and, simply, an alarm or the like was issued to let guards notice.
The photovoltaic power generation systems with solar cells installed on the roofs of general houses have becoming widespread in these years.
In such photovoltaic power generation systems, solar cell modules are connected in series to obtain a desired voltage. This series of solar cell modules is generally called a string. Several strings are connected in parallel to obtain a desired electric current, thus constructing a solar cell array with a power generation scale of desired value. This solar cell array is equipped with components for control and connection of peripheral equipment, thereby composing a photovoltaic power generation system. Accordingly, the solar cell array becomes larger with increase in the power generation scale required of the photovoltaic power generation system, and the number of solar cell modules constituting it also increases. Therefore, in designing of a photovoltaic power generation system, the system is formed by connecting the predetermined number of modules or solar cells of a predetermined area in series and in parallel so as to realize predetermined output voltage and current and a predetermined power generation capacity.
It is feasible to implement power generation with a greater capacity, by increasing the number of series/parallel solar cell modules. However, as the power generation capacity increases, the voltage and current also become larger with increase in the number of series/parallel modules. In general the power generation capability of solar cells is determined by intensity of sunlight incident thereto. Describing it in brief, the photovoltaic power generation system operating at a fixed voltage varies its operating current with variation in insolation (solar radiation) to determine its output power.
The photovoltaic power generation system and the method of protecting the power generation system, described in Japanese Patent Application Laid-Open No. 7-177652, are configured to have a first switch for effecting connection or disconnection between positive and negative power terminals of a solar cell string and output lines connected in parallel thereto and outputting power, a second switch for establishing a short circuit or an open circuit between the power output terminals, and a controller for comparing a voltage value between detection terminals at a predetermined position of the solar cell string, with a predetermined value and controlling switching of the first switch and the second switch, based on the comparison signal. In the photovoltaic power generation system and the method of protecting the photovoltaic power generation system, the solar cell string is judged abnormal when the voltage value between the detection terminals thereof becomes not more than the predetermined value, the power output terminals of this solar cell string are then disconnected from the output lines, and a short circuit is established between the power output terminals, thereby isolating and deactivating the defective solar cell string from the photovoltaic power generation system.
However, in the case of the power plants using the solar cell modules, since the installation scale was large and a large area was necessary, it was difficult to prevent the electric shock hazard only by the conventional means of simply giving an alarm or the like to let the guards note the intrusion of intruder and the number of guards was preferably as small as possible from the aspect of cost. Therefore, the conventional means had a limit.
The solar cell modules used in the photovoltaic power generation systems are usually designed so as to ensure the electrical insulation performance in normal use in the initial stage and after installation. It cannot be denied, however, that there is a possibility of degradation or failure of electrical insulation due to unpredictable causes after installation. There can also occur failure of electrical insulation, for example, due to breakage of the coating over the surface of the solar cell modules, cracks, scars, deformation, etc. of surface glass, and so on for some reason. No one can deny that there is a risk of an electric shock or the like when a man comes to near an exposed portion or a defective portion appearing unpredictably and touches it. The risk of electric shock is high with failure of electrical insulation, particularly, in the case of the large power generation scales, because the voltage and current also become large with increase in the number of series and parallel solar cells, as described previously.
In addition, the solar cell arrays are often installed relatively near the ground with the recent proliferation of the photovoltaic power generation systems, and there is an increasing possibility that a child or a worker not associated with the photovoltaic power generation apparatus (photovoltaic power generation system) touches the solar cell array. It is thus also becoming important to give consideration to prevention of an electric shock. It is the present status that the solar cell array is located within a secure fence and the solar cell array is not allowed to be located at a place which a lot of people go into and out of.
The photovoltaic power generation system and the protection method of the photovoltaic power generation system described in No. 7-177652 were configured to disconnect the solar cell string upon occurrence of disadvantage and no consideration was given to the safeguard against intruders. No consideration was given to malfunctions of the protection system, e.g., in the case of weak insolation, either.
The present invention has been accomplished in order to solve the above-stated problems and it is an object of the present invention to provide photovoltaic power generation systems with high safety and of low cost that can prevent an electric shock hazard of an intruder intruding into a restricted area or the like in the photovoltaic power generation system and that does not have to be always monitored by a manager or a person concerned, and methods of controlling such photovoltaic power generation systems.
Another object of the present invention is to provide a method of controlling a photovoltaic power generation system with high safety while taking account of the installation site and installation method of the solar cell modules.
For achieving the above objects, provided according to a first aspect of the present invention is a photovoltaic power generation system comprising a solar cell module, a restricted area including an area in which the solar cell module is installed, detecting means for detecting intrusion of an intruder into the restricted area to output a signal, and electric shock preventing means activated by the signal outputted from the detecting means.
Provided according to a second aspect of the present invention is a method of controlling a photovoltaic power generation system comprising a solar cell module, a restricted area including an area in which the solar cell module is installed, detecting means for detecting intrusion of an intruder into the restricted area, and electric shock preventing means, wherein when the detecting means detects the intrusion of the intruder into the restricted area, the electric shock preventing means is activated based on a signal outputted from the detecting means.
In the first and second aspects of the present invention, the photovoltaic power generation system preferably comprises means for preventing the intrusion of the intruder into the restricted area.
Provided according to a third aspect of the present invention is a method of controlling a photovoltaic power generation system comprising a solar cell array comprised of a plurality of solar cell modules connected, one sensor or a plurality of sensors arranged around the solar cell array, and a switch for establishing a short circuit between output terminals of the solar cell array, wherein the short circuit between the output terminals is established based on an output signal from the sensor.
It is preferable that the short circuit between the output terminals be established when the output signal of the sensor is not more than a predetermined value.
Provided according to a fourth aspect of the present invention is a method of controlling a photovoltaic power generation system comprising a plurality of solar cell strings each consisting of a plurality of solar cell modules, a plurality of sensors arranged around each of the solar cell strings, and a plurality of switches for establishing a short circuit between output terminals of each of the solar cell strings, wherein the plurality of solar cell strings are connected in parallel and the short circuit between output terminals is established on a string-by-string basis for the plurality of solar cell strings, based on output signals from the plurality of sensors.
It is preferable that when output signals from some of the plurality of sensors are not more than a predetermined value, the short circuit between output terminals be established for each of solar cell strings corresponding to the sensors having outputted the output signals of not more than the predetermined value.
Provided according to a fifth aspect of the present invention is a method of controlling a photovoltaic power generation system comprising a solar cell string comprised of a plurality of solar cell modules connected, a plurality of sensors provided around the solar cell string, and a switch for establishing a short circuit between output terminals of the solar cell string, based on output signals from the plurality of sensors, the method comprising:
a first step of measuring the output signals from the plurality of sensors;
a second step of normalizing values of the output signals;
a third step of calculating a comparison calculated value D, which is defined below, when at least one of a plurality of normalized output signal values Ax is larger than a reference value S,
the comparison calculated value D=(a minimum of the plurality of normalized output signal values Ax)/(a maximum of the plurality of normalized output signal values Ax); and
a fourth step of establishing the short circuit between the output terminals by the switch when the comparison calculated value D is smaller than a comparison reference value D0.
It is preferable that an alarm be issued before the short circuit between the output terminals is established.
Provided according to a sixth aspect of the present invention is a method of controlling a photovoltaic power generation system comprising a plurality of solar cell strings connected in parallel, each solar cell string being comprised of a plurality of solar cell modules connected and having a plurality of sensors provided around the solar cell string and a switch for establishing a short circuit between output terminals of the solar cell string, the method comprising:
(1) carrying out for each of the plurality of solar cell strings,
a first step of measuring output signals from the plurality of sensors,
a second step of normalizing values of the output signals, and
a third step of calculating a comparison calculated value Dy, which is defined below, when at least one of a plurality of normalized output signal values Ax is larger than a reference value S,
the comparison calculated value Dy=(a minimum of the plurality of normalized output signal values Ax)/(a maximum of the plurality of normalized output signal values Ax); and
(2) carrying out a fourth step when at least one of the comparison calculated values Dy of the plurality of solar cell strings is smaller than a comparison reference value D0,
the fourth step being a step of establishing a short circuit between output terminals of a solar cell string corresponding to the comparison calculated value Dy smaller than the comparison reference value D0, by the switch.
It is preferable that before the short circuit is established between the output terminals of the solar cell string corresponding to the comparison calculated value Dy smaller than the comparison reference value D0, an alarm be issued for the solar cell string.
It is also preferable that the sensors be comprised of solar cells.
With the photovoltaic power generation system and the control method thereof according to the first and second aspects of the present invention, guards do not have to always monitor intruders and upon detection of an intruder the guards do not have to instantly go to the place and activate a safeguard such as prevention of an electric shock or the like. Therefore, the number of guards can be reduced. Further, the safety is ensured for the intruders. The detecting means issues a signal at the same time as the detection of the intruder and the signal activates the electric shock preventing means such as means for establishing an entire short circuit or an entire open circuit, e.g., for every module or for every safety voltage, or means for establishing a short circuit for every string. Therefore, the intruder can be prevented from receiving an electric shock, without spending a long time from the detection of the intruder to activation of the safeguard.
In the photovoltaic power generation system according to the first and second aspects of the present invention, the means for preventing the intrusion of the intruder is preferably a stockade, a wall, a fence, or a ditch. This keeps the intruder from readily making access to the restricted area and thus makes it feasible to prevent an electric shock hazard and an accident reaching the electric power system.
It is also preferable that the means for preventing the intrusion of the intruder be double means for preventing the intrusion. This makes it harder for the intruder to readily enter the restricted area than in the case of the single means for preventing the intrusion, and makes it feasible to better prevent the electric shock hazard and the accident reaching the electric power system.
It is also preferable that the detecting means be provided on the inside means for preventing the intrusion of the intruder out of the double means for preventing the intrusion of the intruder. This can decrease malfunctions in detection of intruders, as compared with configurations wherein the detecting means is provided on the single means for preventing the intrusion or wherein the detecting means is provided on the outside means for preventing the intrusion out of the double means for preventing the intrusion, and thus the operating rate of the photovoltaic power generation system can be increased.
In the photovoltaic power generation system and the control method thereof according to the first and second aspects of the present invention, the detecting means is preferably a proximity sensor, an optical sensor, a magnetic sensor, a magnet sensor, a temperature sensor, a humidity sensor, an impact sensor, an acceleration sensor, a weight sensor, a current sensor, or an electromagnetic sensor. When either of these electronic sensors is used, the detection accuracy is enhanced and centralized monitoring can be performed. Therefore, the number of guards can be reduced and, besides, it also becomes easier to ensure the safety for intruders. In addition, the guards do not have to always monitor the intruders and upon detection of an intruder the guards do not have to activate the safeguard such as prevention of an electric shock or the like every time. Therefore, the period from the detection of intruder to the activation of the safeguard can be reduced more whereby the intruder can be prevented from receiving an electric shock.
The electric shock preventing means is preferably means for bringing the solar cell module or a solar cell string consisting of solar cell modules connected in series, into a short-circuit state. This enables the system to be shut down immediately without breaking the photovoltaic power generation system and further renders the voltage null at each part of the series solar cell modules, whereby the intruder can be prevented from experiencing a hazard such as an electric shock or the like. Besides, it becomes feasible to restore the normal operation to the system immediately after confirmation of safety.
It is also preferable that a circuit breaker be provided in the electric shock preventing means to disconnect the solar cell module or the solar cell string from the photovoltaic power generation system to deactivate the module or the string. This configuration can prevent the intruder from experiencing a hazard such as an electric shock or the like, without damaging the photovoltaic power generation system and makes it feasible to reset the system immediately after confirmation of safety.
It is preferable that at least two solar cell strings be connected in parallel to constitute a solar cell array.
The electric shock preventing means preferably has a function of releasing an electric shock preventing action.
As described above, the photovoltaic power generation system and the control method thereof according to the first and second aspects of the present invention are directed toward the system that can safely stop the function of the power generating system itself in order to prevent the intruder from receiving an electric shock by the simple method in the power plants and others using the solar cell modules. More specifically, a power plant itself is provided with means for terminating the power generating system itself in order to ensure the absolute safety under a condition in which there exists no high voltage in the array, for ensuring the safety of people. Since the structure with emphasis on maintenance is important under such environments as the power plants, the safety is also ensured for the intruders and others in the system optimized for the structure.
When the photovoltaic power generation system and the control method thereof according to the first and second aspects of the present invention are applied, particularly, to the power plants, it is necessary to lower the cost of the solar cell modules as much as possible. A conceivable means for lowering the cost is decrease in materials making the solar cell modules. Since the photovoltaic power generation system used in the power plant can be equipped with some measures for preventing people except for operators from entering the interior of the plant, as a hazard controlled area, there is a high possibility that necessary insulation is not so high, different from the conventional solar cell modules, and emphasis is placed on maintainability. Therefore, the live portions are preferably exposed and a coating material making the solar cell modules is laid only near each cell. It is thus contemplated that the cost can be largely curtailed down to a minimum and there arises no problem even with some degradation of safety, e.g., exposure of live portions in part. Namely, the inventors found that simple coatings were enough and effective for the solar cell modules under such special environments as the power plants, thus accomplishing the invention below.
In the photovoltaic power generation system and the control method according to the first and second aspects of the present invention, the solar cell module is preferably installed so that a photovoltaic element provided in an outermost surface on the light-receiving side is exposed directly to the atmosphere. This configuration causes no energy loss of incident light due to absorption and/or reflection by the surface coating or the like, whereby the incident light can be efficiently converted to electricity.
It is also preferable that the solar cell module have a coating only on the outermost surface on the light-receiving side. This can largely decrease the material cost and even if a solar cell is broken it can be readily replaced with another.
It is also preferable that the solar cell module be coated at least on a module-by-module basis on the light-receiving side. This can enhance weatherability of solar cells. When a solar cell is broken, replacement thereof is easy, because only the coating can be peeled off from the defective solar cell. Besides, cost for replacement can be reduced greatly.
In the photovoltaic power generation system the live portions are preferably exposed in part. This permits a manager to readily find a defective module whereby workability of inspection can be improved remarkably.
The control method of the photovoltaic power generation system according to the third aspect of the present invention further comprises the following features: the short circuit is established between output terminals of the solar cell array when the output signal of the sensor is not more than a predetermined value; an alarm is issued before the short circuit is established between the output terminals of the solar cell array; when the output signal of the sensor is not more than a predetermined value, an alarm is issued and thereafter the short circuit is established between the output terminals of the solar cell array after a lapse of a predetermined time; the short-circuit state between the output terminals of the solar cell array is retained before a release operation is carried out.
The control method of the photovoltaic power generation system according to the fourth aspect of the present invention further comprises the following features: the short circuit is established between output terminals of each string when an output signal of a sensor for each string of the solar cell array is not more than a predetermined value; an alarm is issued before the short circuit is established between output terminals of each string of the solar cell array; when an output signal of a sensor for each string of the solar cell array is not more than a predetermined value, an alarm is issued and thereafter the short circuit is established between output terminals of each string after a lapse of a predetermined time; a short-circuit state between output terminals of each string of the solar cell array is retained before a release operation is carried out.
In the control method of the photovoltaic power generation system according to the third and fourth aspects of the present invention, when output signals from the sensors laid around the solar cell array are detected and when it is determined that a human shadow is detected in a local part of the array from the signals, the switch between terminals of the array or a string are controlled to short the array or the string. Even if there is breakage of the surface coating or an insufficient insulation portion such as a crack, a scratch, deformation, etc. of surface glass in the solar cell module, a shock hazard can be prevented when a man touches that part.
In the first to fourth aspects of the present invention, it is also preferable that the solar cell module have a coating only on the outermost surface on the light-receiving side. This permits remarkable reduction of material cost and in the event of disadvantage in a solar cell it can be replaced readily.
It is also preferable that the solar cell module be coated at least on a module-by-module basis on the light-receiving side. This permits improvement in weatherability of solar cells and in the event of disadvantage in a solar cell replacement thereof can be done readily, because only the coating of the defective solar cell can be peeled off. Besides, the cost for the replacement can be reduced remarkably.
In the photovoltaic power generation system the live portions are preferably exposed in part. This permits the manager to readily find a defective module whereby the workability of inspection can be improved remarkably.
In the fifth and sixth aspects of the present invention, the signals of the respective sensors are compared with each other, whereby the shock hazard can be prevented while preventing malfunctions such as unwanted output of alarm, an unwanted short circuit of the solar cell array or the solar cell string, and so on. In this case, it is preferable to issue an alarm before the short circuit is established for the solar cell array or the like.
The configurations and effects of the present invention will be described hereinafter in detail with reference to the drawings.